How do kidneys work?

Your kidneys remove waste products and excess fluid from your body.

What are kidneys?

Your kidneys are two bean-shaped organs, each about the size of a fist. They sit just below your rib cage, one on each side of your spine.

Their main function is to remove waste products and excess fluid. Your blood supply circulates through your kidneys about 12 times every hour. As it goes through your kidneys, it is filtered to remove waste. 

The kidneys turns this waste and excess fluid into urine (pee). Each day your kidneys process around 200 litres of blood.
(Kidney Quality Improvement Partnership, 2016)​

What do kidneys do?

The kidneys are powerful chemical factories that:

  • remove waste products from your body
  • balance your body's fluids
  • release hormones that regulate blood pressure
  • produce an active form of vitamin D that promotes strong, healthy bones
  • control the production of red blood cells
  • remove medicines from your body.

How do kidneys work?

Each kidney is made up of about a million filtering units called nephrons. Each nephron filters a small amount of blood. The nephron includes a filter, called the glomerulus, and a tubule.

The nephrons work through a two-step process. The glomerulus lets fluid and waste products pass through it, but prevents blood cells and large molecules, mostly proteins, from passing.

The filtered fluid then passes through the tubule, which sends needed minerals back to your bloodstream and removes wastes. The final product becomes urine (pee).

A healthy kidney can greatly increase its work capacity. With two healthy kidneys, each one performs 50 per cent of the normal kidney function. If one kidney is lost, the other kidney can enlarge and provide up to 75 per cent of the normal kidney function (the work of one and a half normally functioning kidneys).

Why is it important to take care of my kidneys?

Because of their vital role in keeping your body functioning, it's important to take care of your kidneys. If you don't protect them, you may be at risk of acute kidney injury or chronic kidney disease.

Key ways you can do this are to make healthy lifestyle choices, get your blood pressure checked, manage your diabetes if you have it, drink enough fluid each day and manage your medicines. Read more about how to protect your kidneys.

(World Kidney day, 2018)

Learn more

Kidneys – how they work
Kidney health


  1. The kidneys and how they work National Institute of Diabetes and Digestive and Kidney Diseases, US, 2018

Reviewed by

Dr Hari Talreja is a renal physician/hypertension specialist with advanced training from Canada and a master’s degree from Harvard University in the USA. He is one of the very few American Society of Hypertension-certified hypertension specialists in New Zealand. He is the clinical lead for transplantation, hypertension and clinical research at Counties Manukau Health. He also practises at Ormiston Specialists Centre, Flatbush and Gilgit Road Specialist Centre, Epsom.
Credits: Health Navigator Editorial Team. Reviewed By: Dr Hari Talreja, Specialist Renal and Hypertension Services, Auckland Last reviewed: 09 Jun 2020